[Rivet-announce] Rivet 2.5beta testing release, with prototype detector smearing and beam-boost features

[Andy Buckley]

Dear Rivet users,

We are very pleased to announce a first beta-testing release of Rivet 
2.5, with three major new developments that we think users will be happy 
about:

1) Addition of simple (but very flexible and efficient!) detector 
smearing machinery, mainly for use in BSM analyses.

2) Tools to easily calculate Lorentz transformations to boost into the 
beam centre-of-mass system (for fixed-target and cosmics analyses)

3) Elimination of the Boost library in favour of C++11. A technicality, 
but a nice one!


USING THE BETA

To try out this beta release, you can follow the usual "Getting started" 
instructions from the Rivet web page 
(https://rivet.hepforge.org/trac/wiki/GettingStarted), but using the 
2.5.0beta1 bootstrap script:
 
http://rivet.hepforge.org/hg/bootstrap/raw-file/2.5.0beta1/rivet-bootstrap

Since the new release requires C++11, you will need to ensure that your 
environment has a capable compiler before running the script. Then it 
should "just work". Let us know if you require assistance.


Now a few more details on the two new physics features:


DETECTOR SMEARING:

We have added new SmearedParticle and SmearedJet projection classes. 
Examples of these in use can be found in the new EXAMPLE_SMEAR analysis:
https://rivet.hepforge.org/trac/browser/src/Analyses/EXAMPLE_SMEAR.cc
They are very simple and flexible: the SmearedParticles projection can 
be wrapped around any particle-finding projection (e.g. a FinalState), 
while the SmearedJets wraps around any JetAlg -- in practice this will 
almost certainly be FastJets. This nicely decouples the smearing from 
the usual physics object operations.

Both smearing classes are configured with objects that parameterise 
reconstruction efficiencies and kinematic/identification/tagging 
inaccuracies: you can write your own functions for this, including C++11 
line lambda functions if you like that sort of thing, but we imagine 
that most people will want to use the standard set of LHC detector/reco 
smearings encoded in Rivet:
https://rivet.hepforge.org/trac/browser/include/Rivet/Tools/SmearingFunctions.hh

This way of doing things means that each analysis routine can apply the 
smearings and efficiencies appropriate to its "epoch" of the detector 
and reco software, and the ID/tagger working points used in the data 
analysis. Thanks to our usual automatic projection caching, when running 
many analyses from the same epoch each smearing will be performed only 
once, keeping us computationally efficient.

Please try this out and let us know what you think, and if there are 
extra features you'd love us to provide, or behaviours of this beta that 
you'd rather we change. And if you need any help with getting it 
working, do drop us an email and we'll help out.


BEAM BOOSTS:

To make Rivet friendlier for asymmetric beam analyses, we have removed 
an old feature which would automatically rotate the event to ensure that 
the +z beam was a proton. This was originally added to work-around a 
limitation in Fortran HERWIG for HERA analyses, but is now more of a 
problem than a solution. We have also provided tools to easily calculate 
a LorentzTransformation into the beam centre-of-mass frame -- for example:

#include "Rivet/Projections/Beam.hh"
...
const LorentzTransform beamboost = beamCMSTransform(event);
Particles fsparticles = myfinalstate.particles();
for (Particle& p : fsparticles)
     p.transformBy(beamboost);

Something similar can be done to transform Jet objects into the beam 
frame -- or by any LorentzTransform you happen to calculate. It's not 
rocket science, but it is significantly more user-friendly than what's 
been available so far.

We hope to build boost features directly into projections in future, 
which will be even more convenient, but that requires a bit of careful 
engineering and we hope that this stop-gap solution will make life 
easier for several users. Please try it out and give us some feedback!


Best wishes and we hope you enjoy the new features. Do get in touch :-)

The Rivet team

-- 
Dr Andy Buckley, Lecturer / Royal Society University Research Fellow
Particle Physics Expt Group, University of Glasgow